OP, I don't own a X3 but in the past owned several BMW's including a 335i vert, 540i and 530i. All were reliable but I follow a regular maintenance program. The 3.5 engine (in the X3) has been around for a bit and the X3 is almost at the LCI point. Therefore most of the issues, if any, should be behind. Difficult to forecast 10-years down the road but a BMW can be a long-term reliable vehicle.
I like the styling of the Ranger Rover Evoque but in general, R.R.'s haven't been reliable vehicles. Also consider that if you want to trade 4-6 years down the road depreciation could be a factor.
I don't have any background on the GLK. You may want to check the M-B forums.
Between the GLK and X3, I think it comes down to styling, drive and general feel. Which one better suits your life-style.